Grain Shape and Abrasion of the Gravels on the Gravel Beach of the Shikimi Coast in Nagasaki City

摘要

In this gravel beach（photo 1）, the most abundant gravel are cobbles. To consider the grain shape, we measured the long, intermediate and short axes of the cobbles. Grain size is expressed as the intermediate value, the grain sizes of 100 cobbles in １m2 are 4.0 ～ 13.5 ㎝（fig.1）． Zingg’s classification of grain shape are examined（fig.2）． The relationship between grain size and sphericity of the cobbles is not clear（fig.3）． 　 We set the bricks and andesites on the gravel beach. These bricks and andesites might be shifted to the north by the waves. Abrasion of the bricks and andesites are 8.1 ～ 8.4% （13 days） and 5.4 ～ 4.3%（29 ～ 62 days） respectively（fig.4, table 2, photo 5）.